Selective coating of a balloon catheter with lubricious material for stent deployment

ABSTRACT

A predetermined arrangement of differentially lubricious areas on a balloon catheter for controlling against unexpected movement of a stent carried thereon when in situ in the body.

RELATIONSHIP TO OTHER APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 09/971,435, filed Oct. 4, 2001, now U.S. Pat. No.6,458,138, which is a continuation application of U.S. patentapplication Ser. No. 08/740,727, filed Nov. 1, 1996, now U.S. Pat. No.6,306,144, which are herein incorporated by reference.

FIELD OF THE INVENTION

The invention pertains to the manufacture of a stent carrying ballooncatheter having a predetermined arrangement of differentially lubriciousareas on the balloon catheter to prevent unexpected movement of thestent when in situ in the body and to insure precise stent deployment.

BACKGROUND OF THE INVENTION

This invention relates to stent carrying balloon catheters, sometimesreferred to as dilatation catheters, for use in angioplasty and othervarious vessel repair procedures. Angioplasty has become recognized asan efficient and effective method of opening stenoses in the vascularsystem. In the most widely used form of angioplasty, a balloon catheteris guided through the vascular system until the balloon, which iscarried at the distal end of a catheter shaft, and which may carry anexpandable stent, is positioned across the stenosis or lesion, i.e.,vessel obstruction. The balloon is then inflated to apply pressure tothe obstruction which is essentially remolded by pressing it against theinner wall of the vessel whereby the vessel is opened for improved flow.Due the expansion of the balloon, the stent, which is situated on theballoon, is also expanded and released to aid in support and/or repairof the vessel wall.

Balloon catheters are of various types. One type is fed over a guidewire (i.e., “over-the-wire” catheters) and another type serves as itsown guide wire (i.e., “fixed-wire” catheters). Variations of these twobasic types also have been developed such as the so called “rapidexchange” type, “innerless” catheters, and others. As used herein, theterm “balloon catheter” is meant to include all of the various types ofangioplasty catheters which carry a balloon for performing angioplastyand any other type of stent carrying balloon catheter. Balloon cathetersmay also be of a wide variety of inner structure, such as differentlumen design, of which there are at least three basic types: triplelumen, dual lumen and co-axial lumen. All varieties of internalstructure and design variation are meant to be included by use of theterm “balloon catheter” herein.

When used in percutaneous transluminal coronary angioplasty (PTCA), theballoon catheter is typically advanced through a guide catheter to apreselected vessel location, such as the aorta, for example. Usingfluoroscopy, the surgeon manipulates the catheter until the balloon islocated across the stenosis or obstruction. As already pointed out, thismay involve the use of a guide wire over which the catheter is moved oralternatively the catheter may act as its own guide wire, depending onthe particular design. The manipulation of the stent carrying ballooncatheter through the guide catheter and through the vessels to theobstruction requires the balloon catheter to have a number of differentfeatures.

One such feature is the use of a lubricious coating over the exteriorsurfaces of the catheter and balloon to facilitate movement of thecatheter through the sometimes tortuous paths within the vascular systemto the preselected vessel location for performing the angioplasty. Awide variety of such lubricious coatings have become commonplace for usewith respect to catheters and other devices which are insertable intothe body in connection with surgical procedures and the like. All suchcoatings are intended to be included herein with respect to the use ofthe term “lubricious coating”. Examples of such coatings includesilicone and most preferably hydrophilic coatings involving hydrogelpolymers or the like, such as polymer networks of a vinyl polymer and anuncrosslinked hydrogel, for example. Polyethylene oxide (PEO) is apreferred hydrogel. A preferred vinyl polymer is neopentyl glycoldiacrylate (NPG). Such compositions are more fully disclosed inco-pending U.S. patent application Ser. No. 07/809,889 which is assignedto the same assignee as is the present invention and which isincorporated herein by reference.

These coatings have even been known to include certain agents such asdrugs which may be permanently entrapped in the coating or leachabletherefrom into the body. For example, heparin has been used in such afashion. Heparin is well known as an agent which is often used toinhibit clot formation in the blood. Again, the term “lubriciouscoating” is meant to include all such variations.

One problem with a stent carrying balloon catheter having a lubriciouscoating is that during location and release of the carried stent, thestent tends to slip off the balloon due to the lubricious coating on theballoon. Coating both the shaft and balloon of the catheter inhibits thedoctor's ability to locate, activate and deploy stents at any particularlesion. The stent is sometimes worked off the balloon portion during theinsertion of the catheter and during the expansion of the balloon. Thisunexpected movement of the stent might be regarded negatively by asurgeon. The present invention provides for more secure connectionbetween the balloon and the stent to prevent such slippage. Thus, thoughhigh lubricity is desirable for general movement, it is also desirableto provide a means of anchoring or positioning the stent in a fixedlocation on the balloon so as to avoid unexpected movement thereof uponthe balloon during positioning and expansion.

SUMMARY OF THE INVENTION

The invention is a stent delivery catheter which has a lubriciouscoating on the shaft and, either, partial or no lubricious coating or anadhesive coating, or a combination thereof on the balloon. Thelubricious coating, which is preferably hydrophilic, provides lubricityto the catheter while the uncoated or partially coated or adhesivecoated balloon is able to retain the stent during positioning andrelease without concern for coating induced slippage. This isaccomplished by the present invention through the selective arrangementof lubricious and/or adhesive coatings on the balloon catheter in whichat least a portion of the balloon body is uncoated or less slippery ortacky while a relatively more lubricious coating is placed on at least asubstantial portion of the catheter shaft extending in a proximaldirection from the balloon toward the proximal end of the cathetershaft.

Generally then, the invention contemplates an improvement in thearrangement of lubricious coating(s) and/or adhesive coating(s) on thecatheter to avoid stent slippage and to better anchor the stent inposition for performing angioplasty or other vessel repair. This isaccomplished by what may be termed herein as “differential coating” or“selective lubricating”. By this is meant that the lubricious propertiesof the catheter are selectively designed or constructed and arranged ina predetermined manner such that the catheter shaft i.e, substantiallyall of the catheter generally exhibits more lubricity than the balloongenerally. In short, the catheter is more slippery than the balloon,relatively speaking. It can be seen that an important feature of theinvention lies in the uncoated or less slippery balloon or portionthereof relative to the rest of the catheter so that the stent is morecontrollable.

Such an arrangement may be accomplished in a number of different ways.For example, in one embodiment, a lubricious coating may be providedover substantially the entire catheter, except for the balloon per se.In this embodiment, the balloon does not include any lubricious coatingat all. The stent, which is placed over the balloon, is therefore notsusceptible to slippage due to the greater coefficient of friction thana balloon with lubricant might have.

The balloon also may be coated partially or with a less lubricious orless slippery coating than the coating covering the shaft of thecatheter. In such an instance, two different coatings may be used, suchas a PEO composition as aforementioned on the catheter shaft and soforth, while a silicone coating is placed on the balloon per se. Theballoon may also have specific areas coated, while leaving othersuncovered to provide suitable contact with the stent.

In another variation, different compositions of PEO may be used on theshaft and balloon. In the PEO compositions aforementioned, comprised ofPEO and NPG in isopropyl alcohol and water, variations in the amount ofPEO content affect the final lubricity of the composition; the higherthe percentage PEO, the higher the lubricity. Therefore, one may utilizea relatively higher percentage PEO composition on a catheter shaft and arelatively low percentage composition on the balloon to achieve the endsof this invention also i.e., “differential” or “selective” lubricityover a catheter. Of course, other compositions may also be utilized inthis way.

Another embodiment comprises a coated catheter shaft, coated ballooncones and a coating on at least the distal waist of the balloonextending to the distal catheter tip, the balance of the balloon bodyhaving no coating or one of less lubricity.

In an additional embodiment, both the proximal and distal balloon conesare so coated similarly to the catheter shaft or at least the distalcone. In accordance with the invention, the balance of the balloon bodyis uncoated or coated with a relatively less lubricious coating.

In still a further embodiment, the balloon is partially or entirelycoated with a tacky adhesive.

The advantage of the present invention is the ability to have a coatedcatheter which offers ease of movement through the vasculature alongwith the ability to effectively engage and deploy stents at anyparticular lesion without slippage or premature activation.

BRIEF DESCRIPTION OF THE INVENTION

A detailed description of the invention is hereafter described withspecific reference being made to the drawings in which:

FIG. 1 is a diagrammatic showing of a balloon catheter in which theballoon is positioned across an obstruction in a vessel prior toinflation and an expandable stent is positioned over the balloon.

FIG. 2 is a diagrammatic showing of the positioned balloon catheter ofFIG. 1 with the balloon inflated against the obstruction and the stentexpanded.

FIG. 3 is a schematic showing of a typical balloon catheter, having astent loaded thereon.

FIG. 4 is a schematic diagram showing the basic anatomy of a catheterballoon coated according to one preferred embodiment of the inventionand a stent loaded thereon.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show a stent carrying balloon catheter, generallyindicated at 10, of the over-the-wire type having a guide wire 12 overwhich the catheter has been moved within a vessel 14 to the location ofan obstruction 16. As can be seen in the Figures, balloon 18 and stent17 are positioned across obstruction 16 while the balloon 18 isuninflated (shown in FIG. 1). Upon inflation (shown in FIG. 2), as theballoon expands and exerts pressure against stent 17 and obstruction 16,it is possible for the stent to slip out of place, either forward orbackward along the balloon, if care is not taken to make sure thecatheter is in a fixed position. As shown in FIG. 2, if the catheter isheld in a fixed position, the expanding balloon expands the stent 17 andpresses against obstruction 16 molding it against the inner walls ofvessel 14 to open the vessel. This method is also used for a collapsedor damaged vessel. In such a case, the expanded stent supports thevessel wall and/or repairs damaged tissue. As already indicated withrespect to the present invention, the surface of balloon 18 showncontacting stent 17 is best not coated, or coated with a less lubriciouscoating than the catheter proper, or coated with an adhesive, in orderto provide an “anchoring” effect so that the balloon engages the stent.This is more fully described hereinbelow with reference to FIGS. 3 and4.

By “anchoring” the stent 17 to the balloon 18 according to theinvention, the stent 17 is also prevented from slipping off during thenavigation of the balloon through the body to the targeted area. Priorto the present invention, when the balloon was coated with a lubriciouscoating along with the majority of the rest of the catheter, the loadedstent had a tendency to slip off the balloon or be shifted out of place.This effect is due to the vessel wall and other obstructions which actas a drag on the carried stent as it is transported to the targetedarea. The present invention remedies this problem.

FIG. 3 shows a typical stent carrying balloon catheter which mayincorporate any of the various aforementioned design variations forcatheters. For purposes of understanding the present invention it isonly important to note that catheter 10 includes a balloon generallyindicated at 18, a stent 17, a distal tip 20, a shaft 22 and a manifoldportion generally indicated at 24. Shaft 22 is comprised of a proximalend portion 26 and a distal end portion 25 where it joins balloon 18.Shaft 22 preferably is made from Nylon-11 and low and high densitypolyethylene.

As can be seen in FIG. 4, balloon 18 includes a body portion 30, aproximal cone portion 36, a proximal waist portion 38, a distal coneportion 32 along with a distal waist portion 34 and a stent 17 loadedthereon.

In accordance with one embodiment of the selective arrangement of thelubricious coatings on the catheter as contemplated herein, such acoating is shown at 40 extending over proximal cone 36 (optional), in aproximal direction over shaft 22 toward the proximal end portion 26thereof to thereby cover a substantial portion of shaft 22. Coating 40is also optionally included on the distal cone 32, distal waist portion34 and the distal tip of the catheter 20 as can be seen best in FIG. 4.The balance 30 of the balloon is either uncoated or coated with a lesslubricious composition or coated with an adhesive. The absence of alubricious coating on the balloon allows the stent 17 to remain morefirmly in contact with the balloon itself. The balloon may be partiallycovered with lubricious material as long as a portion of the balloon isuncoated, or coated with a less lubricious material, in order to firmlyhold the stent in place.

As is known in the art with respect to balloon catheters and lubriciouscoatings, the coating will be relatively thin and preferably bonded tothe catheter body surfaces, although not necessarily. Silicone is anexample of an unbonded lubricant. The PEO based coating cited earlier isan example of a bonded one. In the Figures, the relative thickness ofcoating is greatly exaggerated for clarity. However, in accordance withstandard practices in the art, such coatings may nominally be of athickness on the order of 20-50 μm or less and will be applied in avariety of ways depending on the type of coating involved and theparticular selective arrangement of the coating desired. For example, inthe case of various polymeric hydrophilic coatings it has been foundconvenient to utilize an elastic mask to block the body portion of theballoon from being coated with the slippery hydrophilic coating. Themask, in a preferred form, is a heat shrink polyolefin sized to providea slight interference fit around the balloon to keep the mask in placeduring processing. In one preferred form, the uncoated length of thearea masked has been about ⅝″ of an inch centered on the body portion ofthe balloon and extending around its peripheral surface. Such anarrangement is indicated in FIG. 4. Of course, at least some of body ofthe balloon is left uncoated as well or coated with a relatively lesslubricious coating than the balance of the catheter proper. Preferably,the entire balloon portion which is in contact with the stent is leftuncoated.

Upon completion of the polymer coating procedure, the mask is thenremoved to expose the uncoated balloon body portion. In such anarrangement, the shaft and balloon cones and waists, being unmaskedduring the coating procedure, are coated with the same slippery coatingas is placed on the rest of the catheter. As is already known, suchcoatings are typically applied to the catheter surfaces in the form of asolution which is allowed to dry and is subsequently cured usually byheat or Ultraviolet light for a short period of time.

Other means for achieving the selective placement of coating(s) on thecatheter may include the use of a release agent such as an oil which maybe spread over the area which it is desired will remain uncoated. Aftercuring of the coating, this area is then exposed by simply peeling thecoating off the area carrying the oil. Also, if desired, one may rinseor wipe a portion of the coating off the balloon before the coating iscured. Another alternative is to modify the coating in the area of theballoon which is to remain uncoated such as using an ultravioletblocker.

A final selective coating arrangement according to the invention mayalso be made by first coating with a less slippery, compatible coatingover the balloon and possibly more of the catheter, then masking,applying highly slippery coatings as desired and proceeding as normal orvice versa.

This invention is equally applicable to balloons of the compliant typeand to those of the non-compliant type. A wide variety for the materialsof the balloons is well known, some examples of which, to name a few,include ethylene vinylacetate copolymer polyethylene terephthalate,polyethylene, polyolefin copolymer and high density polyethylene.

Masking materials are most conveniently heat shrink polyethylene onmandrels of sizes appropriate to the particular balloon and are placedthereon. The coating may comprise a mix of a higher molecular weightsoluble polymer such as PEO and a UV curable diacrylate in isopropylalcohol and water containing a trace of photoinitiator. The coatingsolution is wiped onto selected areas of the catheter device which isthen passed to a UV chamber, purged of oxygen, exposed to UV and thenremoved. The mask is removed, the area is cleaned ultrasonically with awater bath to remove any drips. The uncoated portion of the balloon isleft as is or a less lubricious coating is applied to it such assilicone or a polymer coating with a lesser percentage of hydrogelcontent. Other methods of application will be known to those familiarwith the art.

In a further embodiment of the invention the balloon exhibits differentfrictional characteristics in its inflated and non-inflated states. Theballoon catheter has a low coefficient of sliding friction in a deflatedstate and a higher coefficient of friction in a inflated state. Theballoon has a high coefficient of sliding friction in a deflated statefor facilitating the transport of a contracted stent and a lowercoefficient of friction in an inflated or expanded state. Furtherdisclosure of such balloon surface and material characteristics can befound in U.S. patent application Ser. No. 08/609,274, filed on Mar. 1,1996, which is incorporated herein by reference.

In accordance with one aspect of this invention a medical balloon isformed of a thin material for expansion from a compact state to anexpanded state in a patient's vessel. The balloon is formed with a firstmaterial portion or spaced first material portions such that the balloonin its compact state essentially exposes the exterior surfaces of onlythe first material portion or portions. In the expanded state theballoon exposes the exterior surfaces of both the first and remainingmaterial portions for contact with surrounding vessels. The exteriorsurface on a first material portion has an integral surface with acoefficient of friction that differs from the coefficient of friction ofthe exterior surface of a remaining portion of the balloon.

In accordance with another aspect of the referenced invention a stentdelivery system includes a catheter with an inflation lumen, and amedical balloon formed of a thin material positioned at the distal endof the catheter in communication with the inflation balloon so theballoon is expansible from a compact state to an expanded state inresponse to the injection of an inflation fluid through the inflationlumen. A first material portion or a plurality of first spaced materialportions are located so that the balloon essentially exposes theexterior surfaces of only the first material portion or portions in itscompact state. As the balloon expands, it expands the stent and exposesthe exterior surfaces of the first material portion and of the remainingmaterial portion. The exterior surface of a first material portion has acoefficient of friction that is greater than the coefficient of frictionof the exterior surface of the remaining portion of the balloon, suchthat the balloon in its compact state engages and provides friction tohold the stent in place on the balloon and in its expanded statefacilitates the release of the balloon from the stent.

In a further embodiment of the present inventive concept, the balloonitself may be coated either partially or completely, but at least inareas in which a loaded stent would have contact with, with a tackycomposition which aids in retaining a loaded stent in place during thetortuous location of the stent at a target position of a vessel. Theballoon is coated with an adhesive, such as an elastomeric basedadhesive, i.e. polyisobutylene, and pressure sensitive-type adhesives,i.e. polyamides and polyacrylate, making the surface of the balloonwhich would be in contact with a loaded stent tacky. The bond which iscreated between the coated balloon and loaded stent is only strongenough to prevent slippage of the stent, but is weak enough to releasewhen the balloon is expanded. The portions of the balloon which arecoated and the tackiness of the adhesive may vary to achieve thisresult. One such pattern involves coating longitudinal strips along theballoon which are accessible for engagement while the balloon isdeflated. A similar pattern can be seen in U.S. patent application Ser.No. 08/609,274, as discussed above. With such a pattern, it iscontemplated that the exposed surface area when the balloon is collapsedwould be coated with adhesive to achieve a selective tacky coating onthe balloon. Preferably, the balloon is coated by a tacky coating or acoating with a high coefficient of friction, i.e. a static coefficientof friction of about 0.2-0.4. The coating utilized to coat the balloonshould be of higher coefficient of friction than the coating used tocoat the shaft.

Preferably, the adhesive used is a aqueous dispersion of ethylene vinylacetate (EVA) or a water-based dispersion based on high-molecular weightethylene interpolymers, such as ADCOTE® 37P147, which is manufactured byMorton®. The major use for Adcote 37P147 is as an in-line laminatingadhesive, a primer, or as a base for compounding coatings and adhesives.Adcote 37P147 is suggested for applications which require the propertyof low temperature heat activation and hot tack. This product exhibitsgood adhesion to Mylar, polyethylene, polypropylene, aluminum foil andPVDC coated glassine. For surface coating, Adcote 37P147 must becompounded. Typical Dispersion Properties are: Solids—45%; Viscosity—500cps; pH—10; and Weigh/Gallon—8.2 lbs. The dispersion is stable in mostalkaline systems, but may coagulate under acidic conditions. Adcote37P147 exhibits good storage stability, but mixing just prior to use isrecommended in order to assure product uniformity. Freezing conditionsshould be avoided as freezing will coagulate the dispersion. Standardcoating techniques, such as wire-wound rods and gravure, can beemployed. However, as these dispersions are water-based, care should betaken to minimize the generation of foam. If a tendency to foam occurs,the addition of 0.05-0.2% (based on wet dispersion weight) of Foamkill614 (Crucible Chemical Company, Donaldson Center, Greenville, S.C.29605) or Adcote 7R1 is recommended. The dispersion may be reduced withwater, preferably slightly basic (buffer solution of about ph 10), if alarge amount is to be added. Drying should be effected by heat givingrise to an approximate surface web temperature of 150-180° F. Coatingweights for adhesive use of 1.0-2.0 lbs/ream is adequate for mostapplications.

While this invention may be embodied in many different forms, there areshown in the drawings and described in detail herein specific preferredembodiments of the invention. The present disclosure is anexemplification of the principles of the invention and is not intendedto limit the invention to the particular embodiments illustrated.

This completes the description of the preferred and alternateembodiments of the invention. Those skilled in the art may recognizeother equivalents to the specific embodiment described herein whichequivalents are intended to be encompassed by the claims attachedhereto.

1. A balloon catheter having a shaft and a balloon associated therewithand a stent carried on said balloon, the balloon having a proximal endportion, a distal end portion and a central portion positioned betweenthe proximal end portion and the distal end portion, wherein the stentis positioned over the central portion, the central portion having afirst layer disposed exteriorly thereon, the first layer on the centralportion being exposed to the stent, the distal end portion having afirst layer disposed exteriorly thereon, the first layer on the distalend portion being exposed, wherein the first layer on the centralportion has a higher coefficient of friction than the first layer on thedistal end portion the proximal end portion, having a first layerdisposed exteriorly thereon, the first layer on the proximal and portionbeing exposed, wherein the first layer on the central portion has ahigher coefficient of friction than the first layer on the proximal endportion and wherein the first layers on the distal and proximal portionsof the balloon form one layer and cover the entire balloon, such that itis between the balloon and the first layer on the central portion. 2.The balloon catheter of claim 1, wherein the shaft is coated with alubricious hydrophilic coating, the first layer on the central portionhas a higher coefficient of friction than the coating on the shaft. 3.The catheter according to claim 2, wherein the coating on the shaftcomprises a polyethylene oxide composition.
 4. The balloon catheter ofclaim 1, further comprising a distal tip, the distal tip being distal tothe balloon, wherein the first layer on the central portion of theballoon has a higher coefficient of friction than the distal tip.
 5. Theballoon catheter of claim 1, wherein the first layer on the centralportion is tacky.
 6. The balloon catheter of claim 1, wherein the shaftis coated with a lubricious hydrophilic coating, the first layer on thecentral portion has a higher coefficient of friction than the coating onthe shaft.
 7. The balloon catheter of claim 6, wherein the first layerson the proximal and distal portion of the balloon is the same as thecoating on the shaft.
 8. The catheter according to claim 1, wherein thefirst layer on the distal end portion comprises silicone.
 9. In a stentcarrying balloon catheter of the type including a shaft, a balloonhaving a proximal cone, a distal cone and a central portion between theproximal cone and the distal cone, a distal tip portion, the distal tipbeing distal to the balloon, a stent positioned on the balloon over thecentral portion, the central portion having a first layer disposedexteriorly thereon, the first layer on the central portion being exposedto the stent, the distal cone having a first layer disposed exteriorlythereon, the first layer on the distal cone being exposed, wherein thefirst layer on the central portion has a higher coefficient of frictionthan the first layer on the distal cone, the proximal cone having afirst layer disposed exteriorly thereon, the first layer on the proximalcone being exposed, wherein the first layer on the central portion has ahigher coefficient of friction than the first layer on the proximal coneand wherein the first layers on the distal and proximal cones of theballoon form one layer and cover the entire balloon, such that it isbetween the balloon and the first layer on the central portion.
 10. Thestent carrying balloon catheter of claim 9, wherein the first layer onthe central portion is tacky.
 11. The stent carrying balloon catheter ofclaim 9, the shaft being coated with a lubricious hydrophilic coating,wherein the first layer on the central portion has a higher coefficientof friction than the coating on the shaft, first layer on the proximalcone and the first layer on the distal cone.
 12. The stent carryingballoon catheter of claim 9, wherein the shaft is coated with alubricious hydrophilic coating and wherein the first layer on thecentral portion has a higher coefficient of friction than the coating onthe shaft.
 13. The stent carrying balloon catheter of claim 9, whereinthe first layer on the central portion of the balloon has a highercoefficient of friction than the distal tip portion.
 14. The stentcarrying balloon catheter of claim 9, the shaft being coated with afirst layer, wherein the first layers on the shaft and the distal andproximal cones comprises the same materials.